In English, to think is a general term, while to ponder, to contemplate, to surmise, etc. are related to thinking but are more specific. 
Hebrew works the same way, with לַחְשׁוֹב (lahkh-SHOHV) meaning to think, and other words denoting something more specific. For example, the Biblical and Modern Hebrew לַהֲגוֹת (lah-hah-GOHT) means to pronounce, but also to ponder. Likewise, הִגָּיוֹן (hee-gah-YOHN), in Biblical Hebrew, refers to the act of pondering (תְּהִלִּים י”ט – Psalms 19).
In Medieval times, the study of logic became a central discipline for scholars. So for Jewish scholars, the word הגיון took on a meaning even more specific than pondering – it came to mean logic, which is what the word means to this day.
That which is logical is הֶגְיוֹנִי (heh-gyoh-NEE). For example, זֶה הֶגְיוֹנִי שֶׁהַשֶּׁמֶש שׁוֹקַעַת כָּל יוֹם (zeh heh-gyoh-NEE sheh-hah-SHEH-mesh shoh-KAH-aht kohl yohm) – It’s logical that the sun sets every day.